Roof membranes usually made of an elastomeric single sheet material are increasingly being used for commercial and industrial flat roof installations. There is a continuing problem with such waterproofing membrane systems in that they become disengaged or damaged as the result of wind uplift forces, a condition associated with changes in atmospheric pressure.
In order to prevent this from happening, a variety of methods are used to prevent the membrane from being disturbed by wind uplift forces. One of the common ones is the use of stone ballast. In such a method the waterproofing membrane is completely covered with stone ballast aggregate (usually 3/4" to 2 1/2" in size), at the rate of approximately 10 pounds per square foot. This has the potential disadvantage of exceeding the design dead-load of the structure, thus restricting the live-load capacity of existing roof decks and supporting structure. Also, due to wind movement, the stone ballast can shift. The ballast thus fails to perform satisfactorily and permits the membrane to billow causing, in some instances, stone to be ejected from the rooftop, resulting in potential damage or injury to property or persons and ultimately resulting in the waterproofing membrane becoming damaged or disengaged.
Another system involves mechanical affixing the waterproofing membrane and subcomponents thereunder with threaded fasteners throughout the field of the roof in a predetermined pattern. Approximately 65 percent of commercial and industrial buildings utilize steel decks. When threaded fasteners are used to secure the waterproofing membrane and subcomponents to the steel decks, they experience lateral as well is vertical loads induced by wind uplift forces. Since the steel decks are usually 18 to 20 gauge in thickness, they offer a minimum of net area for thread engagement. Membrane billowing and steel deck flutter are typical effects of wind uplift forces. This causes threaded fasteners to become disengaged, ultimately backing out and leaving the membrane unsecured. When fasteners back out from steel decks, they frequently cause puncturing of the waterproofing membrane when the roof is subjected to live loads. Further, corrosion of the threaded fasteners and/or the structural steel deck results. Even with the use of noncorrosive threaded fasteners, corrosion occurs at the steel deck around the thread engagement of the fastener due to thermal conductance and an associated dew point. This not only results in the failure of the waterproofing membrane securement system, but also in structural damage to the steel deck.
Another securement system used is fully to adhere the waterproofing membrane with an adhesive to the top surface of a subcomponent which has been mechanically affixed to the roof deck. This method of roof membrane securement to a subcomponent has inherent disadvantages. Membrane subcomponents must first be mechanically affixed to the structural deck by means of threaded fasteners. Subcomponent materials, such as insulating materials, are frequently sensitive to moisture and condensation, permitting separation of subcomponent top surface at the interface of the adhesive bond. The adhesive bond between waterproofing membrane and subcomponent top surface is subjected to shear forces as a result of expansion and contraction of the membrane. The adhesives are extremely sensitive to moisture and temperature. The adhesive bond failure at the interface of the subcomponent and the waterproofing membrane results in the loss of membrane securement.
Another system involves the use of ballast boards. In this system, the waterproofing membrane is restrained with a ballast board of extruded closed cell polystyrene insulation having tongue and groove sides and a cementitious mortar topping. The total weight is approximately 4.5 pounds per square foot. This weight, in some cases, exceeds the design dead-load. Consequently, it restricts live-load capacity of existing roof decks. The membrane subcomponents must first be mechanically affixed to the structural deck by means of threaded fasteners with all subcomponent joints taped. The tongue and groove integrity of ballast boards is paramount in providing wind uplift resistance. Extensive metal strapping or concrete slabs, sometimes referred to as pavers, are required to secure the ballast board around the perimeter of roof and where tongue and groove integrity has been interrupted. Should the membrane billow, loose or disengaged ballast boards can be ejected from the roof, causing personal injury and property damage. In addition, the waterproofing membrane can then become damaged or disengaged.